In-Water Voltage Gradient Detector

ABSTRACT

A voltage gradient detector provides notice when a potentially hazardous voltage gradient is present in water, employing at least one pair of spaced-apart electrodes connected to an LED. The electrode spacing is selected such that, when exposed to a sufficiently large voltage gradient, the voltage between the electrodes causes activation of the LED. The LED can provide visual illumination, or can be a part of a switching device such as a photoMOS relay that in turn activates an alarm device such as an audible sounder or a high-intensity light. Sensitivity in multiple directions can be attained by employing a pair of LEDs between the electrodes, and by employing three pairs of electrodes and associated LED pairs, with the pairs of electrodes being spaced apart along substantially orthogonal axes. These pairs may be discrete or may share an electrode in common.

FIELD OF THE INVENTION

The present invention provides a voltage gradient detector for providingnotice of the presence in water of a voltage gradient greater than aspecified strength.

BACKGROUND OF THE INVENTION

Electrical gradients in water can create risks of electrocution andelectroshock drowning if an individual enters water in which asufficiently strong voltage gradient is present. Such hazardousconditions can occur in swimming pools, hot tubs, spas, and Jacuzziswhich have improperly installed, poorly maintained, or otherwise faultyunderwater lighting, heaters pumps, wiring, or other electricallyoperated equipment or appliances. Currently, protection againstelectrocution and electroshock drowning hazards in such facilitiesdepends mainly upon the use of GFCI (ground fault circuit interrupter)circuit breakers being installed on AC power lines. However, suchcircuit breakers may not be present in older facilities, which are alsosubject to greater risk due to deterioration over time of wiring forunderwater equipment. There are also possibilities of risk at locationsin more open water, where voltage gradients may be present due to fallenelectrical transmission lines, current leakage from boats, or othervoltage sources.

One device that has been developed for providing an indication of ACvoltage gradient strength in seawater is the Voltage Gradient Probemarketed by Online Electronics Ltd. of Aberdeen, Scotland, UK. Thisdevice is described as a hand-held, subsea unit for providing an easilyinterpreted indication of AC electric field strength in seawater toindicate to divers or ROVs the presence of any local AC electric fieldswhile working on subsea electrical equipment. The device appears to belimited to active use, and detects only AC voltages. Furthermore, thedevice is described as having a typical battery life of 10 days, makingit ill-suited for passively monitoring a location to provide a warningwhen a voltage gradient is present in the water at that location.

A less critical risk is caused by voltage gradients that cause increasedcorrosion of vessels or other equipment that are immersed in water wheresuch a gradient is present. Such gradients can greatly accelerate damagedue to electrolytic corrosion or galvanic corrosion, and thus detectingsuch gradients is of particular interest to operators of marinas andother areas where vessels are present.

SUMMARY OF INVENTION

The present invention is a device for monitoring voltage gradients inwater, particularly to provide detection of such gradients so as to warnwhen a potentially dangerous gradient is present. One application thathas particular utility is to provide notice to individuals that thewater should not be entered because the gradient would place anindividual therein in danger of death or serious injury. A rudimentarydevice which is well suited for placing an individual on notice of ahazardous voltage gradient has a pair of spaced-apart electrodes thatare maintained at a separation S, and a light-emitting diode (LED)connected therebetween by a set of conductors.

The separation S and response characteristic of the LED are selectedsuch that the LED emits light when the voltage difference between thetwo electrodes has reached or exceeded a target threshold level. Basedon the minimum voltage gradient of concern, the separation S of theelectrodes can be selected so that, in combination with the responsecharacteristic of the LED, the LED illuminates to provide notice of anendangering level for individuals. Typically, for an LED having anactivation voltage of V_(LED) to provide notice of a minimum gradient ofconcern G_(MIN), the separation S should be set such that:

S _(MIN) >V _(LED) /G _(MIN)

Typically, the LED is connected in series with a resistor to limitcurrent, in which case the voltage between the electrodes that is neededto illuminate the LED is an effective activation threshold voltageV_(T), and this activation voltage is used to determine the minimumseparation.

This threshold voltage V_(T) includes the LED activation voltage V_(LED)as well as the voltage drop across the resistor under the minimumactivation current for the LED (the current draw of the LED at theminimum activation voltage V_(LED)). To maintain the sensitivity of thegradient detector in such cases, the resistance value of the resistor isselected so that, when the resistor is in series with the LED, theresistor results in only a small increase in the voltage gradient neededto illuminate the LED.

To assure a set separation S and that the potential experienced by theLED is measured between the electrodes, the electrodes can be mounted tothe extremities of a spacer. The spacer can be hollow so as to provide awatertight central cavity that provides a sealed passageway for the setof conductors that connect the electrodes to electrical contacts of theLED. Providing a sealed housing for the conductors and the electricalcontacts of the LED serves to electrically isolate these elements fromthe water when the voltage gradient detector is in service, therebyassuring that any voltage gradient along the length of the spacer isexperienced as a potential between the electrodes. It should beappreciated that the conductors connecting the electrodes to thecontacts of the LED could be run external to the body if the conductorsand their connections to the electrodes and electrical contacts of theLED are isolated by watertight casings, in which case the spacer neednot be hollow.

Since the LED is responsive to only one polarity of the voltagegradient, when the voltage to be detected is DC, it is preferred to usepairs of opposed LEDs so that either polarity of the voltage gradientcan be monitored without requiring a user to reorient the device. Thisarrangement allows the device to effectively monitor either an increaseor a decrease in potential with regard to the X direction, since apositive gradient in one direction causes a positive voltage differencebetween the electrodes to illuminate one LED, while a voltage gradientin the opposite direction illuminates the other LED that is connected inparallel to the same electrodes, but in reverse. The LEDs could bedifferent colors to allow a user to readily determine the voltagegradient direction. The use of such paired LEDs should also betterindicate when an AC voltage gradient is present, since both LEDs will beilluminated in this case. The pair of LEDs could be provided by a singlebi-color LED unit that generates red light for a DC voltage in onepolarity, green light for DC voltage in the opposite polarity, andapparent yellow light for AC voltage.

For personal safety applications, where the voltage gradient of concernhas been found to be 2V/foot, the minimum separation S of the electrodesto provide the threshold voltage for activating LEDs (which is typically1.6V) is in the neighborhood of 8-9 inches; however, it may be desirableto increase this distance to provide a margin of safety. When theseparation S is set to provide a sufficient voltage to illuminate theLEDs, there is no need to amplify the voltage, and such devices canoperate without the need for external power, with the LED powered onlyby the voltage gradient in the water.

In addition to employing a series resistor, the likelihood of burningout the LED(s) can be further reduced by providing a Zener-diode-basedvoltage limiter between the electrodes and the LEDs to prevent voltagesapplied to the LEDs from reaching or exceeding levels that would causeburnout or other damage to the LEDs. Typically, such a voltage limiteremploys a pair of reversed Zener diodes connected in series with aresistor to provide protection for AC voltage gradients and/or for DCvoltage gradients in either direction with respect to the electrodes.

The above devices require no power to provide a visible signal. However,when only the gradient itself is used to power the device, the intensityof the signal (the visible light emitted) is relatively small andrequires direct observation to detect the presence of a gradient.

When a stronger visual signal is sought, or when a non-visual signalsuch as an audio warning or a transmitted signal warning is desired, theLED can be provided as part of a photoMOS relay for closing a switchthat can either activate a brighter light, an audio alarm, and/orprovide some other form of warning such as a transmitted message to abase receiver. These warning devices may require a significant amount ofpower, but only when activated. LED-based photoMOS relays are commonlyavailable for use as opto-isolators. In this case, it would also bepossible to employ an LED that emits light at a frequency in theinfrared range, which typically allows a lower activation thresholdvoltage. When photoMOS relays are employed to switch on an alarm device,it may be desirable to also provide a pair of visible light LEDs to helpthe user identify whether the voltage gradient is due to DC or ACvoltage, in order to aid in identifying the character of the voltageresponsible for the gradient.

While the discussion of the use of the above device has been fordetecting the presence of voltage gradients in water that could bepotentially harmful to individuals, lower values of voltage gradientscan be harmful to structures or vessels as a result of increasedelectrolytic corrosion action where the potential results from voltage(current) leakage from vessel to vessel or vessel to docking structure.While there is no bright line gradient level that results in suchcorrosion problem, significant corrosion risk can result from gradientsthat are in the neighborhood of 0.1V/ft to 1.0 V/ft. At even lowergradients, galvanic corrosion action can occur where the water allows acurrent to flow between dissimilar metals, creating a galvanic cell.Again, there is no bright line value where such corrosion becomessignificant, but frequently such can be a problem when the gradient isin the neighborhood of 0.01V/ft to 0.1V/ft. To detect these lower-valuegradients requires modification of the geometry of the device and/oradditional elements to increase the voltage experienced by the LED(s).

Adjustment of the potential experienced by the LEDs can be done bychanging the separation between the electrodes, in which case increasingthe separation increases the voltage difference experienced by the LEDsfor a particular gradient. Alternatively, the voltage experienced by theLEDs can be increased by using an amplifier to amplify the voltagepresent between the electrodes and providing the output of the amplifierto the LEDs. This option requires power to operate to the amplifier.

While the above discussion has been for devices which are designed to beresponsive to a gradient in a direction selected by the user, it isfrequently preferred to have a device with the ability to respond tovoltage gradients with less dependency on the particular orientation ofthe electrodes. For such applications, three sets of orthogonal orsubstantially orthogonal sensor pairs can be employed. Such electrodepairs could be provided by discrete pairs of electrodes or by two orthree of the pairs sharing an electrode in common, in which case thedetector could employ as few as four electrodes. Having a commonelectrode shared by three pairs of electrodes may have particularbenefit when the voltage is amplified, as it can allow a single multipleamplifier device to be used to simplify the circuitry needed to powerthe amplifiers. The use of a shared common electrode also assures thatthe sensitivity to gradients is with respect to a common point. Analternative to using a shared electrode would be to have one electrodefrom each pair connected by a common lead; however, to avoid creatingthe effect of reduced separation resulting from such a commonconnection, the connected electrodes should be located in closeproximity to each other.

The angle between the axes along which the pairs are separated should bebetween 45° and 135°. To reduce dependency on the direction of a voltagegradient that may be present, the angles between the axes of separationshould preferably be within about 10° of 90°. In situations where thepairs are separated along axes that are skewed, rather thanintersecting, the angle between any two axes in question can be definedas the angle between one axis and a vector that is parallel to the otheraxis and intersecting the first.

These devices can be floating devices which do not require interactionwith a user, and such devices have particular utility for determiningvoltage gradients in a confined volume such as a pond or a pool. For usein ponds, the structure for holding the electrode pairs at a separationcan be shrouded so as not the be snagged by debris if the device isfloated. When the device is floated, ballast may be desirable so as toavoid overturning in the water as the device moves about.

Similarly, the detector could be configured as a submersible device thatrests on the bottom of a body of water, is secured to an anchor orunderwater structure, is affixed to the hull of a boat, or is attachedto a submersible device such as a pool-cleaning vacuum device such thatthe entire device, or the sensors of the device, are located at aselected depth below the surface of the body of water.

For other applications, it is frequently advantageous to provide ahand-operated device, that can sense gradients in three orthogonaldirections. To facilitate location of the source of the gradient, it maybe preferred to have the electrode pairs arranged such that one pair isseparated along a substantially vertical axis, while the other two pairsdefine a substantially horizontal plane, and to have separate LEDs toindicate the presence of a voltage gradient along each of these threeaxes. In one embodiment, such a device has an extender between theelectrode pairs and a grip portion that is held by the user, allowingthe user to readily immerse the electrode pairs. A hand-held device hasparticular utility when monitoring gradients in the vicinity of a vesseland/or a stationary structure in the water, such as a dock, to detectgradients likely to cause accelerated corrosion damage. As discussedabove, the gradients of concern in such cases can be substantially lowerthan those which endanger a person, and there is no critical value belowwhich there is no corrosion. For such use, the device can be fitted withswitches and contacts can be attached to the electrodes to allow theLEDs to be disconnected from the electrodes and to allow a voltmeter tobe attached in place of the LEDs. Having this capacity allows the userto measure the gradient and thus to evaluate the severity of thecorrosion problem and the need for prompt attention to correct theproblem. When amplifiers are employed to increase the voltageexperienced by the LEDs, it may also be desirable to provide a switch toallow the LEDs to receive either the output from the amplifiers or theunamplified voltages across the electrode pairs.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a section view of one embodiment of the present inventionwhich employs a single visible-light LED to monitor the voltagedifference between a pair of electrodes maintained at a fixed separationS. In this embodiment, the separation S is selected to provide a targetthreshold level for the voltage differential between the electrodeswhich results in illumination of the LED.

FIG. 2 is a section view of an embodiment similar to the embodiment ofFIG. 1, but which employs a pair of LEDs connected in parallel withreverse polarity so that voltage gradients can be monitored in eitherdirection, and to more clearly indicate the presence of an AC voltagegradient.

FIG. 3 is an isometric view of an embodiment where the separation Sbetween the electrodes can be adjusted which, in turn, allows one toadjust the voltage generated between the electrodes for a particulargradient. This allows the user to increase the separation S, therebyincreasing the voltage until it is sufficient to light one of the LEDs.In some embodiments, it may be preferred to have the separation S smallto avoid a voltage difference large enough to damage the LEDs and havethe user adjust the distance until the LEDs illuminate; then, knowingthe separation, the user can determine the voltage gradient.

FIG. 4 is a sectioned view of an embodiment that provides a secondaryset of wiring and a switch that disconnects the electrodes from the LEDsand instead connects them to a voltmeter so that the voltage between theelectrodes can be measured.

FIG. 5 is an isometric view of a handheld device having three orthogonalpairs of electrodes that reside below the water when in service;however, the device has sufficient buoyancy to reside near the surfaceand thus aid in the ease of manual movement of the device by a user.Each of the electrodes is connected to an associated pair of LEDs, sothat a sufficiently strong voltage gradient in any direction results ina voltage between the electrodes of at least one of the pairs thatcauses illumination of at least one of the LEDs associated with thatpair of electrodes. The gradient detector also has a voltmeter that canbe selectively connected between any one of the electrode pairs to allowthe user to measure the indicated voltage.

FIG. 6 is an isometric view of another embodiment having three pairs oforthogonal electrodes and associated LED pairs, but in this embodimentthese elements are mounted in a spacer that provides a floatableenclosure. Two pairs of electrodes are horizontal and mounted in a ring,while the third pair is mounted normal to the other two pairs andpositioned with respect to a flotation collar such that all pairs ofelectrodes reside below the water when the structure is floated. Thecontour of the floatable device is configured so as to shroud theelectrodes and reduce the likelihood of the electrodes snagging ondebris in the water such as seaweed. The location of the flotationcollar near the top of the device and incorporating a ballast weight orforming the ring of a relatively dense material to mount the horizontalelectrode pairs can provide sufficient ballast to assure the device willnot overturn in normal service.

FIG. 7 is a schematic diagram illustrating an embodiment that employsboth visible-light LEDs and infrared LEDs to indicate the presence of avoltage between paired electrodes sufficient to cause illumination of atleast one of the associated LEDs. Three pairs of electrodes areemployed, and the embodiment could be employed in devices such as thoseshown in FIGS. 5 and 6. The infrared LEDs are incorporated into photoMOSrelays that serve as switches to activate an audible alarm, while thevisible LEDs provide a visual indication when a voltage gradient ispresent. The schematic view also illustrates resistors that areconnected in series with the LEDs in order to limit the current andreduce the likelihood of damage in service.

FIG. 8 is a schematic diagram illustrating an embodiment similar to thatshown in FIG. 7, but where each pair of electrodes has an associatedpair of Zener diodes connected in parallel with the remaining circuitry,along with an associated resister to provide a voltage limiting circuit.These Zener diode voltage limiting circuits serve to set an upper limiton the voltage experienced by the remaining circuitry so as to preventdamage from excessively high voltages across the electrodes.

FIG. 9 is a schematic diagram illustrating another embodiment thatemploys LED-based photoMOS relays, but where no paired visible-lightLEDs are employed. Visual indication of the presence of a sufficientlystrong voltage gradient is provided by a warning light that is switchedon by the photoMOS relays; one suitable warning light is ahigh-intensity LED lamp. The photoMOS relays also switch an audiblealarm. This embodiment also employs amplifiers to increase the potentialbetween the electrode pairs to allow detection of voltage gradients thatwould otherwise be too small to activate the photoMOS relays. Thissensitivity to low voltages makes the device well suited to detectingvoltage gradients associated with increased risk of corrosion.

FIG. 10 is a partial view of an optional modification of the embodimentshown in FIG. 9, corresponding to the region 10. In the modifiedgradient detector, each pair of electrodes is connected to itsassociated amplifier via a switch that allows the electrodes to beconnected either to the input of the amplifier or directly to thephotoMOS relays, allowing the user to select whether the photoMOS relaysrespond to the output of the amplifier or to the unamplified voltage.

FIG. 11 is an isometric view that illustrates a voltage gradientdetector that forms another embodiment of the present invention. Thevoltage gradient detector again has three pairs of electrodes separatedalong orthogonal axes, but in this embodiment the three pairs share acommon electrode. This embodiment also differs in that the separationsbetween the electrodes are not uniform for the three pairs.

FIG. 12 is a schematic diagram illustrating one example of circuitrythat can be employed in an embodiment such as that shown in FIG. 11,having a common electrode shared by three pairs of electrodes. Thecircuit is similar to that shown in FIG. 9, but each pair of electrodeshas one discrete electrode and one electrode that is connected to anelectrode of each of the other pairs. When the separations between theelectrode pairs differ, compensation for such difference could beprovided by differing the gain of the amplifiers to provide a moreisotropic response of the detector.

FIG. 13 is a partial schematic view of a modification to the circuitshown in FIG. 12, where the three amplifiers for the electrode pairs areprovided by a single multiple-amplifier device. The use of a singledevice simplifies the connections needed to power the amplifiers, asonly one set of power connections is needed, rather than three as whenseparate amplifiers are employed.

FIG. 14 is an isometric view of a voltage gradient detector that formsanother embodiment of the present invention, and which is designed to besubmerged when in service. The detector again has three pairs ofelectrodes that share a common electrode and are separated alongorthogonal axes, but in this embodiment the axes are inclined withrespect to the horizontal plane and vertical axis. Because it isdesigned to be submerged when in service, an ultrasonic transmitter isemployed to provide a warning of the presence of a voltage gradient, theultrasonic transmitter generating a signal that is received by a remotereceiver with a submerged ultrasonic sensor and which, in turn, providesan audible or visible alarm in response.

FIG. 15 is a diagram of the electrodes of the embodiment shown in FIG.14, illustrating their positions at four adjacent corners of a cube.

FIG. 16 illustrates a modification of the voltage gradient detectorshown in FIG. 14, where the position of the common electrode has beenelevated with respect to the discrete electrodes of the pairs. Thismodification results in angles between the axes that are less than 90°.

FIG. 17 illustrates another modification of the voltage gradientdetector shown in FIG. 14, where the position of the common electrodehas been moved closer to the plane in which the discrete electrodesreside. This modification results in angles between the axes that aregreater than 90°.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an isometric view of one embodiment of an in-water voltagegradient detector 10 of the present invention. For reasons discussedbelow, the gradient detector 10 has characteristics that make itsuitable for providing notice to an individual when the voltage gradientin the direction measured is above a threshold level where an individualentering the water would be likely to be harmed by the voltage gradient.The device 10 has a pair of spaced apart electrodes 12 that aremaintained at a separation S by a hollow spacer 14, to which theelectrodes 12 are sealably attached.

An LED 16 resides between the electrodes 12, and is sealably attached tothe spacer 14 such that its electrical contacts can be connected to thefirst pair of electrodes 12 by a pair of conductors 18. The sealableattachment of the electrodes 12 and the LED 16 to the spacer 14 servesto electrically isolate the electrodes 12 from each other, except fortheir connection through the LED 16 via the conductors 18. The spacer 14has a central cavity 20 through which the conductors 18 are strung Theconductors 18 connect to the LED 16 such that, when a voltage differenceis maintained between the two electrodes 12, the LED 16 experiences thevoltage difference. The sealable attachment of the electrodes 12 and theLED 16 to the spacer 14 serves to encapsulate the central cavity 20 toisolate it from the water, and thus the electrical connection betweenthe electrodes 12 and the electrical connectors of the LED 16 iselectrically isolated from the water.

When this device is placed in water having a voltage gradient ofmagnitude G and orientation in the direction of the measurement suchthat the voltage difference exists between the electrodes 12, the LED 16is subject to a potential and, if this potential exceeds a targetthreshold for activation, the LED 16 illuminates; this threshold voltagefor activation results from the electrodes 12 being at the thresholdpotential and, since the electrode separation S is known, the voltagegradient can be calculated.

V _(ELECTRODES) =G*S

If the activation voltage V_(LED) of the LED 16 is known, the separationS can be set such that V_(ELECTRODES)≧V_(LED) to cause illumination ofthe LED 16 when the voltage gradient reaches the danger value, and thusillumination of the LED 16 provides notice that it is unsafe to enterthe water.

For example, according to one source, an AC voltage gradient of 2V/footis sufficient to create a risk of harm to an individual in the water.For a detector employing a visible red LED with an activation thresholdvoltage V_(LED) of 1.6 volts, a separation S between the electrodes of0.8 feet should result in illumination of the LED when such a voltagegradient is present and aligned along the separation of the electrodes;various embodiments discussed below illustrate how the limit ofdirectionality can be overcome. To provide a margin of safety, it may bedesirable to set the critical voltage gradient to be detected somewhatlower, and thus to place the electrodes at a greater separation. In theabove example, in order to detect a voltage gradient at 50% of the valuecalculated to cause a risk, the electrode separation would be doubled to1.6 feet so as to cause illumination of the LED when the electrodes areexposed to a voltage gradient of 1V/foot.

FIG. 2 is a section view of a gradient detector 50 that is similar tothe gradient detector 10 shown in FIG. 1, but where the response is lessdependent on the direction of the gradient, and where the detection ofAC voltage gradients is enhanced. The detector 50 again has a pair ofelectrodes 52 which are spaced apart at a separation S by a hollowspacer 54. A first LED 56 is attached and sealed to the spacer 54 andcommunicates with a central cavity 58 in the spacer 54. This centralcavity 58 also communicates with the electrodes 52. In the gradientdetector 50, a second LED 60 is provided which also attaches to thespacer 54 and communicates with the central cavity 58. The LEDs (56, 60)are connected to the electrodes 52 by a set of conductors 62 thatincludes a first pair of conductors 64 that electrically connects thefirst LED 56 to the first pair of electrodes 52, and a second pair ofconductors 66 that connects the second LED 60 to the first pair ofelectrodes 52, but with its polarity reversed from that of the first LED56. Having the first LED 56 and the second LED 60 connected in parallelbut with their polarity opposite with respect to the electrodes 52allows the gradient detector 50 to detect either a positive or negativepotential between the electrodes 52 with respect to a particularorientation if the voltage source is DC. If the source is AC, then bothLEDs illuminate, and for 60 cycle AC, the combined appearance of a redLED and a green LED provides an appearance of a continuous light that isyellow if the LEDs are closely spaced; such close spacing can beconveniently provided by a bi-color LED that includes a red LED and agreen LED in a single package.

FIG. 3 is an isometric view of an in-water voltage gradient detector 100which includes the features of the gradient detector 50 shown in FIG. 2,but which allows varying the separation S between a pair of electrodes102. The electrodes 102 are attached to a hollow spacer 104, to which afirst LED 106 and a second LED 108 are also attached. The gradientdetector 100 differs from the embodiments described above in that thedevice is tunable with respect to the gradient that will be effectivefor providing notice of its presence. This is accomplished by providingthe spacer 104 with a central portion 110 that is slidably and sealablyengaged by a pair of extensions 112 on which the electrodes 102 areaffixed. The slidable engagement of the extensions 112 with the centralportion 110 allows the separation S between the electrodes 102 to beadjusted, and thus adjust the gradient that results in illumination ofat least one of the LEDs (106, 108).

In some embodiments, it may be preferred to have the separation S smallso as to avoid a voltage difference large enough to damage the LEDs, andhave the user adjust the distance until the LEDs illuminate. In suchcases, knowing the separation, the user can determine the voltagegradient. Another benefit from having the separation variable is itallows the spacing to be increased, and thus allow activation of theLEDs at lower gradients. In some cases, this may allow one to determinethe presence of gradients that could result in increased risk ofelectrolytic corrosion.

FIG. 4 is an isometric view of a gradient detector 200 which againincludes features of the gradient detector 50 illustrated in FIG. 2, buthas the additional option of providing a measurement of the voltage. Thegradient detector 200 has a hollow spacer 202 that fixes the separationS of a pair of electrodes 204′, 204″. The spacer 202 has a centralcavity 206 through which a bundle of conductors 208 can pass. One pairof conductors 210 in the bundle of conductors 208 connect the electrode204′ to a pair of reversed-polarity LEDs 212, while a second pair ofconductors 214 connect the electrode 204′ to a voltmeter 216. A thirdpair of conductors 218 connect between the electrode 204″ and atwo-position switch 220. When the two-position switch 220 is in a firstposition, the electrode 204″ is connected to the LEDs 212, and when inthe second position, the switch 220 connects the electrode 204″ to thevoltmeter 216, allowing the voltage difference between the electrodes204 to be measured, rather than merely being indicated as below or abovea threshold level for activation of the LEDs 212. Such measurement canbe particularly beneficial when monitoring for voltage gradientsassociated with corrosion, to provide the user a more sensitiveindication to provide a basis for evaluating the seriousness of thecorrosion risk.

The embodiments discussed above respond to voltage gradients along asingle axis, and thus would not provide notice of voltage gradients thatare oriented such that the electrodes reside at substantially the samevoltage. This limitation can be overcome to some extent by moving thegradient detector to different orientations; however, such isinconvenient and may be difficult to accomplish while allowing the userto remain out of the water, and is not suitable for the gradientdetector intended for passive monitoring. To provide detection of agradient regardless of its direction without requiring active change inthe orientation by the user, multiple pairs of electrodes can beemployed, as discussed for the various embodiments described below.

FIG. 5 is an isometric view of a hand-held voltage gradient detector 300which has the capacity to monitor voltage gradients in three orthogonaldirections (X, Y, Z). The gradient detector 300 has a spacer 302 that isconfigured with a pair of horizontal extensions 304 that extendorthogonally to each other, and a vertical extension 306, which isaffixed orthogonally with respect to both the horizontal extensions 304.Affixed to these extensions (304, 306) are three pairs of electrodes(308, 310, and 312), and the spacer 302 can be hollow to house sets ofconductors (not shown) between the electrodes (308, 310, and 312) ineach pair so as to isolate the conductors from the water when theelectrodes (308, 310, and 312) are immersed. The first pair ofelectrodes 308 are separated along the X-axis by a separation S_(X), thesecond pair of electrodes 310 are separated along the Y-axis by aseparation S_(Y), and the third pair of electrodes 312 are separatedalong the Z-axis by a separation S_(Z). In most cases, it is preferredfor the separations S_(X), S_(Y), and S_(Z) to be equal.

A vertical extender 314 attaches to one of the electrodes 312 and alsoattaches to a grip section 316 which is provided with a handle 318 toallow a user to readily hold the gradient detector 300 and to positionthe electrode pairs (308, 310, and 312) at desired locations below thesurface of the water. The grip section 316 is also provided with a firstpair of LEDs 320, a second pair of LEDs 322, and a third pair of LEDs324, where each of these pairs of LEDs (320, 322, and 324) isrespectively connected between one of the pairs of electrodes (308, 310,and 312) by one of the sets of conductors; this connection can be in amanner analogous to the connection scheme discussed for a single pair ofelectrodes and LEDs in the above discussion of FIG. 2, or in a mannersimilar to the circuits discussed below with regard to FIGS. 7-10.Housing the connections between the electrodes and the contacts of theLEDs in the spacer 302 serves to electrically isolate the LEDs and theconductors from the water when the electrode pairs (308, 310, and 312)are immersed. Preferably, the grip section 316 is also sealed to protectthese components from damage in the event that the entire gradientdetector 300 is inadvertently dropped into the water.

The grip section 316 of this embodiment also houses a voltmeter 326, anda mode switch 328 that can switch the connection of any one of the pairsof electrodes (308, 310, and 312) to the voltmeter 326 rather than tothe associated pair of LEDs (320, 322, and 324). Thus, when the presenceof a voltage gradient is indicated by illumination of one or more of theLEDs (320, 322, and 324), the user can operate the mode switch 328 toconnect the voltmeter 326 to whichever pair of electrodes (308, 310, and312) corresponds to the brightest LED(s) to obtain a measurement of thevoltage between the electrodes (308, 310, and 312). If the separations(S_(X), S_(Y), and S_(Z)) are set equal, the voltmeter 326 could becalibrated to indicate the magnitude of the voltage gradient between theelectrodes (308, 310, and 312). Again, such measurement has particularbenefit when monitoring for voltage gradients liable to cause corrosiondamage.

FIG. 6 is an isometric view of a floating voltage gradient detector 400which shares many features of the voltage gradient detector 300discussed above. The gradient detector 400 is again designed to monitorthe voltage gradient in an X-direction, a Y-direction, and aZ-direction. The gradient detector 400 has a buoyant body 402 thatserves as a spacer, and which is hollow in this embodiment. The body 402has attached thereto a first pair of electrodes 404 which are positionedalong the X-axis, a second pair of electrodes 406 which are positionedalong the Y-axis, and a third pair of electrodes 408 which arepositioned along the Z-axis. The buoyant body 402 is configured with aring 410 to position the electrodes 404 and 406, which are mounted onthe perimeter of the ring 410. The ring 410 provides a convex, roundedstructure, so as to reduce the susceptibility of the hollow body 402 tosnagging on objects in the water.

In addition to the body 402, the gradient detector 400 has a buoyant cap412 attached to the body 402 and positioned such that, when the gradientdetector 400 is placed in the water, the cap 412 resides, at least inpart, above water. Mounted to the cap 412 are a first pair of LEDs 414,a second pair of LEDs 416, and a third pair of LEDs 418; again, thesepairs of LEDs (414, 416, and 418) are connected in parallel withreversed polarities between the three pairs of electrodes (404, 406, and408) in a manner analogous to the connection used for the embodimentshown in FIG. 5, using sets of conductors (not shown) that are housedwithin the body 402 so as to isolate the electrical connections betweenthe electrodes (404, 406, and 408), the LEDs (414, 416, and 418), andthe conductors from the water when the gradient detector 400 is inservice. Ballast (not shown) can be added to the body 402 if necessaryto assure that all electrodes (404, 406, and 408) reside below the waterand that the body 402 does not overturn when the gradient detector 400is in service; however, the ring 410 may be made of a sufficiently densematerial that additional ballast is not needed.

FIG. 7 is a schematic diagram illustrating one example of the circuitrythat could be employed for a 3-directional gradient detector 500 that issimilar to those embodiments shown in FIGS. 5 and 6. The gradientdetector 500 shown in FIG. 7 is designed to provide not only a visualindication of the presence of a sufficiently large voltage gradient, butalso an audible alarm to alert the user that such a gradient is present,thereby providing a greater degree of safety and making the devicesuitable for passively monitoring a region of water.

The gradient detector 500 again has three pairs of electrodes 502 thatare separated along orthogonal axes, with the spacing between electrodes502 being the same for each pair. For each pair of electrodes 502, apair of reversed-polarity visible LEDs 504 are connected, in series witha visible LED resistor 506. The visible LEDs 504 provide a visualindication of when a voltage gradient in the water is sufficientlystrong and is positioned so as to cause the voltage between at least oneof the pairs of electrodes to be at least as great as the thresholdactivation voltage for the associated visible LEDs 504; the thresholdactivation voltage is selected to include the voltage drop across thevisible LED resistor 506 at the minimum voltage that causes one of theLEDs 504 to illuminate.

Connected in parallel with each of the pairs of visible LEDs 504 is apair of photoMOS relays 508, which are connected in parallel to eachother with reversed polarity, and in series with a photoMOS resistor510. Each of the photoMOS relays 508 consists of an infrared LED 512 anda photosensor 514, where the infrared LED 512 responds to voltage acrossthe electrodes 502 in the same manner as one of the visible LEDs 504,and the photosensor 514 acts as a switch that closes when the lightgenerated by the infrared LED 512 is detected. All the photosensors 514are connected to an audible alarm device, in this embodiment a piezosounder 516, and a battery 518. When any of the infrared LEDs 512experiences a voltage sufficient to illuminate it, the correspondingphotosensor 514 acts as a closed switch to allow the battery 518 topower the piezo sounder 516 to provide an audible notice of the presenceof a voltage gradient. When no gradient is present, the photosensors 514act as open switches with only a very small leakage current, allowingthe battery 518 to have a desirably long useful life when the gradientdetector 500 is operating. For example, for six photoMOS relays, eachhaving a 1 μA leakage current when switched “off”, a 3V battery can beemployed to power the piezo sounder, resulting in a power consumption ofonly 18 μW when monitoring.

Because the activation voltage for the visible LEDs 504 is typicallyslightly higher than the activation voltage for the infrared LEDs 512,the values of the visible LED resistors 506 and the photoMOS resistors510 may be adjusted so that both the visible LEDs 504 and the photoMOSrelays 508 are activated by the same voltage potential between theelectrode pair 502 to which they are connected. For example, LEDsemitting visible red light can have an activation voltage as low asabout 1.6V, corresponding to an LED current of about 1 mA, while aphotoMOS relay can have an activation voltage as low as about 1.14V,corresponding to an IR-LED current of about 1.8 mA. However, to preservethe sensitivity of the detector 500, it is typically preferred to allowthe photoMOS relays 508 to activate at a lower activation voltage, andto select the resistors (506, 510) to provide a desired balance betweenhaving a low voltage drop across the resistor (506, 510) when thecorresponding LED (504, 512) is first activated, and having the resistor(506, 510) sufficiently large as to protect the LED (504, 512) fromdamage due to excessive currents under the expected operatingconditions.

For example, for a visible red LED having an activation voltage of 1.6Vand a corresponding current of 1 mA, the associated resistor could beselected to have a value that results in a 0.05V voltage drop at thatcurrent, in which case Ohm's law finds the desired resister value to be50Ω. If the LED has a maximum recommended operating current of 20 mA,the 50Ω resistor will have a voltage drop of 1V at that current. Thus,this combination of the LED and resistor will detect the presence of avoltage gradient that results in a voltage between the electrodes ofover 1.65V, and can be safely operated when the voltage is as high as2.6V.

For the example of an IR-LED typical of those employed in photoMOSrelays, having an activation voltage of 1.14V and 1.8 mA current, aresistor of 28Ω would provide a voltage drop of 0.05V at the minimum 1.8mA current. When the IR-LED has a maximum recommended operating currentof 50 mA, a 28Ω resistor results in a voltage drop of 1.4V, and thus therelay will switch on when the voltage across the electrodes is above1.19V, and can be safely operated up to a voltage of 2.5V. Protectionfrom higher voltages can be provided by a voltage-limiting device, suchas discussed below with regard to FIG. 8. Whether or not such additionalprotection is included, it may be desirable to provide a testing devicethat can engage one of the pairs of the electrodes to apply a specifiedvoltage across the pair in order to periodically verify that LEDs areoperating as intended. Such a testing device could include probes thatcan be spaced at the separation S in order to be placed against aselected pair of electrodes, and could employ a 3-position switch toallow the user to selectively apply a DC voltage in either polarity oran AC voltage. This testing device could be sequentially engaged witheach pair of electrodes to check the operating condition of all theLEDs. When both visible LEDs and photoMOS relays are employed, such atesting device could also allow the user to switch between twoprescribed voltages, one just sufficient to activate the photoMOS relaysand a slightly higher voltage sufficient to illuminate the visible LEDs.

When determining the desired separation between the electrodes, thevoltage drop across the resistor at the minimum operating current of theLED can be simply added to the activation voltage of the LED to providean effective activation threshold voltage that is sufficiently accuratefor this application. In such cases, the separation can be determinedas:

$S_{{MI}\; N} = {\frac{V_{LED} + \left( {I_{LED}*R} \right)}{G_{{MI}\; N}} = \frac{V_{LED} + V_{RESISTOR}}{G_{{MI}\; N}}}$

where V_(LED) is the minimum activation voltage for the LED, I_(LED) isthe current through the LED at the minimum activation voltage,V_(RESISTOR) is the voltage drop across the resistor resulting from thecurrent at that LED voltage, and G_(MIN) is the minimum voltage gradientto be detected. In the case where the minimum voltage gradient to bedetected is 2V/foot, the visible red LED and resistor values providedabove result in a minimum separation between the electrodes of 0.8 feet,while the values for the IR-LED and associated resistor discussed aboveresult in a minimum separation of only 0.6 feet. These relatively smallvalues allow the gradient detector to be conveniently sized.

When a combination of visible LEDs 504 and photoMOS relays 508 areemployed, the photoMOS relays 508 can typically respond in a moresensitive manner to voltage gradients for a particular separation of theelectrodes 502, and can provide an indication such as a high-intensitylight (not shown) and/or audible alarm (piezo sounder 516) that is morereadily noticed by a user. In such cases, the visible LEDs 504 are stillbeneficial in providing an indication of the direction of the gradient,and may also make it easier for the user to determine whether thegradient is caused by an AC or DC voltage. Alternatively, an indicationof DC versus AC voltage could be provided by connecting one of each pairof photoMOS relays to one alarm device and the other of each pair to adifferent device.

FIG. 8 is schematic diagram of another embodiment, of the presentinvention, a gradient detector 500′ that is similar to the gradientdetector 500 discussed above, but where each of the electrode pairs 502has a voltage limiting circuit 520, which consists of a pair of Zenerdiodes 522 connected in parallel with the visible LEDs 504 and thephotoMOS relays 508, and a Zener resistor 524 connected in series. Inthis case, the visible LED resistors 506′ and the photoMOS resistors510′ should have values selected to take into account the addedresistance of the Zener resistors 524.

FIG. 9 is a schematic diagram illustrating another embodiment of thepresent invention, a gradient detector 600 that again employs threepairs of electrodes 602 and associated photoMOS relays 604 that serve asswitches to activate a high-intensity LED 606 that serves as a warninglight, and a piezo sounder 608, both powered by a battery 610. While thegradient detector 600 illustrated does not include visible LEDs, suchcould be readily provided, connected in the same manner as those shownin FIGS. 7 and 8. Similarly, an alternative alarm device could beemployed; one example would be a wireless transmitter that communicatesan alarm notice to a remote receiver. Another alternative would be apair of different alarm devices, such as differently-coloredhigh-intensity LED lamps or piezo sounders set to different frequencies,to help the user identify whether a DC voltage or AC voltage isresponsible for the voltage gradient.

The gradient detector 600 is designed for use to detect gradients thatare lower than those associated with risk of injury to individuals inthe water, but rather those which are likely to cause damage due tocorrosion at an unacceptable rate. Such gradients may be in theneighborhood of about 0.01 V/foot-1.0 V/foot. For each pair ofelectrodes 602, a voltage amplifier 612 is provided, which is poweredbatteries and connections that are not illustrated. The output of thevoltage amplifier 612 is provided to the photoMOS relays 604 associatedwith that pair of electrodes 602. Typically, a gain of about 5× to 500×is felt to be effective. Because the voltage amplifiers 612 requirepower when in operation, the life of batteries powering these amplifiersis much shorter than the life of the battery used in the gradientdetectors (500, 500′) shown in FIGS. 7 and 8. For those detectors thatare designed to float or be affixed to a structure such that theelectrodes are submerged, a photovoltaic solar panel can be employed torecharge the batteries that power the amplifiers 612 to greatly reducethe need to service the detector.

In some cases, it may be desirable for the voltage amplifiers 612 tohave a variable gain to allow the user to set the sensitivity of thegradient detector 600 for a desired application. For example, the usermight first use the gradient detector 600 with the amplifiers 612 set toa relatively low gain to test the water in several desired locations forstrong gradients (in the neighborhood of 0.1V/ft to 1.0 V/ft) caused byvoltage leakage from one vessel to another and/or between a vessel and adocking structure; such gradients are typically associated withelectrolytic corrosion. If no such gradient is detected, the user couldthen set the gain to a higher value to use the gradient detector 600 totest the water alongside a vessel for smaller gradients, in theneighborhood of 0.01V/ft to 0.1V/ft, typically associated galvaniccorrosion action between dissimilar metals in the water.

FIG. 10 is a partial view illustrating an optional modification to theconnection between one of the pairs of electrodes 602 and the associatedamplifier 612 that could be employed in the gradient detector 600. Asshown in FIG. 10, a double-pole double-throw switch 614 is provided,which selectively connects the electrodes 602 either to a first pair ofswitch contacts 616, that are in turn connected to the input of theamplifier 612, or to a second pair of switch contacts 618, which areconnected directly to the photoMOS relays 604 (shown in FIG. 9) so as toprovide the voltage between the electrodes 602 to the photoMOS relays604 without amplification.

FIG. 11 illustrates a voltage gradient detector 700 that again has afirst pair of electrodes 702, a second pair of electrodes 704, and athird pair of electrodes 706. In the detector 700, the three pairs ofelectrodes (702, 704, and 706) share a common electrode 708. A firstdiscrete electrode 710 is separated from the common electrode 708 alonga first axis 712 by a separation S₁, a second discrete electrode 714 isseparated from the common electrode 708 along a second axis 716 by aseparation S₂, and third discrete electrode 718 is separated from thecommon electrode 708 along a third axis 720 by a separation S₃, wherethe three axes (712, 716, and 720) are orthogonal to each other.

As shown in FIG. 11, the electrodes (708, 710, 714, and 718) are affixedto a spacer 722 that provides a housing to maintain the electrodes (708,710, 714, and 718) spaced apart along their respective axes (712, 716,and 720) and to house the circuitry connected to the electrodes (708,710, 714, and 718); one example of circuitry that would be suitable isshown in FIG. 12. When at least one pair of electrodes (702, 704, or706) is exposed to a gradient of sufficient magnitude, the circuitryenergizes a photoMOS relay 724 (shown in FIG. 12) to illuminate ahigh-intensity visible LED 726 mounted on the spacer 722. Alternativewarnings, such as an audible alarm 728 (also shown in FIG. 12) or asignal transmitted to a remote device could also be employed, either inplace of or in addition to the visible LED 726.

The example of circuitry shown in FIG. 12 shares many features in commonwith the circuitry shown in FIG. 9 for the detector 600 discussed above.The detector 700 differs in that each of the electrode pairs (702, 704,and 706) shares the common electrode 708. Thus, a first amplifier 730receives the voltage between the first electrode 710 and the commonelectrode 708, a second amplifier 732 receives the voltage between thesecond electrode 714 and the common electrode 708, and a third amplifier734 receives the voltage between the third electrode 718 and the commonelectrode 708. The output of each of the amplifiers (730, 732, and 734)is provided to one pair of the photoMOS relays 724 that serve asswitches to activate the high-intensity LED 726.

As shown in FIG. 11, the position of the electrodes (708, 710, 714, and718) on the spacer 722 is such that the separation S₃ is substantiallylarger than the separations S₁ and S₂. If the amplifiers (730, 732, and734) have equal gains, this will result in a greater sensitivity togradients along the third axis 720 than along the other axes (712 and716). To provide a more isotropic response, the gain of the thirdamplifier 734 can be made proportionally less than that of the first andsecond amplifiers (730 and 732) to compensate for the increasedseparation and provide a similar response along each axis (712, 716, and720) to a gradient of equal magnitude. It should be appreciated that, ifthe separations were similar and sufficiently large, no amplificationmay be required and a circuit similar to those shown in FIGS. 7 and 8could be employed, but where one electrode of each pair is provided byan electrode that is connected to serve as one of the electrodes foreach pair.

FIG. 13 illustrates a portion of an alternate circuit for the detector700, where a multiple-amplifier 736 is employed to replace theindividual amplifiers (730, 732, and 734) to reduce the number ofconnections needed to provide power to the amplifiers. Such multipleamplifiers are commonly available as integrated circuits, such as aquad-amp IC, of which only three of the four amplifier inputs andoutputs are employed. The use of the single multiple amplifier 736requires that the electrode pairs (702, 704, and 706) share the commonelectrode 708.

FIG. 14 illustrates a voltage gradient detector 800 that forms anotherembodiment of the present invention, and which again employs three pairsof electrodes 802 that each consist of a shared common electrode 804 anda discrete electrode 806. The pairs of electrodes 802 are separatedalong axes 808 (shown in FIG. 15) that are again orthogonal to eachother. The detector 800 differs from the multiple-pair embodimentsdiscussed above in that the axes 808 are not aligned with the horizontalplane or the vertical axis when in service, but rather are inclinedthereto. As better illustrated in FIG. 15, the electrodes (804, 806) arepositioned at four adjacent corners of a cube, with the axes 808defining edges of the cube.

The detector 800 is designed for use while submerged, and has a sealedhousing 810 that serves as a spacer and which contains the circuitryneeded to provide a warning of the presence of a voltage gradient ofsufficient magnitude to be of concern. The circuitry can be similar tothat shown in FIG. 12; however, since the detector 800 is intended forservice while submerged, it is preferred to employ an ultrasonictransmitter 812 that generates a signal suitable for reception by aremote receiver 814 to provide the warning. The remote receiver 814,with a submerged ultrasonic sensor 816, can provide a visual and/oraudible alarm to notify persons in the area that a gradient of concernis present in the water. The detector 800 can be secured to an anchor orunderwater structure, such as a dock pile, or could be attached to asubmerged device, such as a pool cleaning vacuum, that operatesunderwater.

Because the pairs of electrodes 802 are separated along orthogonal axes808 and have the same distance of separation (S₁, S₂, and S₃) betweenthe two electrodes (804 and 806) that form the pair, they provide arelatively isotropic response to gradients throughout the volume ofwater surrounding the detector 800. The response will be strongest for agradient that is along one of the axes 808, and weakest for a gradientthat is inclined to all three axes 808. In this latter case, the weakestsignal for a gradient of a particular strength will still be 58% (1/√3)of the magnitude of a signal for the same strength of gradient directedalong one of the axes 808. In the event that an even more isotropicresponse is desired, such could be achieved by employing additionalpairs of electrodes separated along axes that are inclined with respectto the axes 808.

The directional effect of the positioning of the electrodes can beillustrated by the modified embodiments shown in FIGS. 16 and 17, whichrespectively show detectors 800′ and 800″, where the vertical positionof the common electrodes (804′, 804″) has been adjusted such that theaxes (808′, 808″) are no longer orthogonal to each other. In thedetector 800′, the common electrode 804′ has been elevated relative tothe discrete electrodes 806, with the result that the angles between theaxes 808′ are somewhat less than 90°. This results in a response patternthat provides a stronger signal for a voltage gradient that is verticalthan for a gradient of the same strength that is horizontal. In thedetector 800″, the common electrode 804″ has been moved vertically to alocation closer to the common plane of the discrete electrodes 806,resulting in angles between the axes 808″ that are somewhat greater than90°. This configuration results in a response pattern that provides aweaker signal for a voltage gradient that is vertical than for a similargradient that is horizontal. When a common electrode is employed, theaxes of separation will intersect. When discrete pairs of electrodes areemployed, the axes of separation may be skewed rather than intersecting;in such cases, the inclination of one axis with respect to another isdetermined by the inclination of vectors that are each parallel to oneaxis and which intersect each other.

The directionality of the response increases as the angles divergefurther from 90°, and when the angles approach 45° or 135°, thedirectionality is so great as to provide little or no benefit fromemploying three electrode pairs rather than only one or two. In the caseof the detector 800′, the response would become similar to that of asingle-pair device with the electrodes separated vertically, while inthe detector 800″, the response would become similar to that of adual-pair device with the pairs separated along orthogonal, horizontalaxes. For most purposes, it is felt that maintaining the angles betweenthe axes between about 80° and 100° provides a degree of isotropicresponse close of that of a device employing orthogonal axes.

While the novel features of the present invention have been described interms of particular embodiments and preferred applications, it should beappreciated by one skilled in the art that substitution of materials andmodification of details can be made without departing from the spirit ofthe invention.

What I claim is:
 1. A voltage gradient detector for use in water to detect the presence of a voltage gradient at least as large as a specified critical voltage gradient G_(MIN), the gradient detector comprising: a first pair of electrodes maintained at a separation S₁ along a first axis; at least one first LED with a known voltage characteristic such that said first LED is illuminated when it experiences a set voltage threshold value V_(T1); means for electrically connecting said at least one first LED to said first pair of electrodes in series with a first LED resistor such that said at least one first LED experiences a voltage that is directly responsive to the voltage between said first pair of electrodes and which is at least as great as the set voltage threshold value V_(T1) when said first pair of electrodes, spaced apart at the separation S₁, are in contact with a voltage gradient at least as great as the critical voltage gradient G_(MIN), wherein the set voltage threshold value V_(T1) is calculated by adding the minimum voltage that illuminates said at least one first LED and the voltage drop across said first LED resister that results from the current through said at least one first LED at that minimum voltage; a second pair of electrodes maintained at a separation S₂ along a second axis that is substantially orthogonal to the first axis; at least one second LED with a known voltage characteristic such that said second LED is illuminated when it experiences a set voltage threshold value V_(T2); means for electrically connecting said at least one second LED to said second pair of electrodes in series with a second LED resistor such that said at least one second LED experiences a voltage that is directly responsive to the voltage between said second pair of electrodes and which is at least as great as the set voltage threshold value V_(T2) when said second pair of electrodes, spaced apart at the separation S₂, are in contact with a voltage gradient at least as great as the critical voltage gradient G_(MIN), wherein the set voltage threshold value V_(T2) is calculated by adding the minimum voltage that illuminates said at least one second LED and the voltage drop across said second LED resister that results from the current through said at least one second LED at that minimum voltage; a third pair of electrodes maintained at a separation S₃ along a third axis that is substantially orthogonal to the first axis and to the second axis; at least one third LED with a known voltage characteristic such that said third LED is illuminated when it experiences a set voltage threshold value V_(T3); means for electrically connecting said at least one third LED to said third pair of electrodes in series with a third LED resistor such that said at least one third LED experiences a voltage that is directly responsive to the voltage between said third pair of electrodes and which is at least as great as the set voltage threshold value V_(T3) when said third pair of electrodes, spaced apart at the separation S₃, are in contact with a voltage gradient at least as great as the critical voltage gradient G_(MIN), wherein the set voltage threshold value V_(T3) is calculated by adding the minimum voltage that illuminates said at least one third LED and the voltage drop across said third LED resister that results from the current through said at least one third LED at that minimum voltage; and means for providing a notice when said at least one of said LEDs is illuminated.
 2. The voltage gradient detector of claim 1 wherein the substantially orthogonal relationship between the axes is further restricted such that each is inclined with respect to each of the other two by an angle between 80° and 100°.
 3. The voltage gradient detector of claim 2 wherein each of said first, second, and third pairs of electrodes has a discrete electrode and a common electrode, and wherein said common electrode is connected to each of, said means for electrically connecting said at least one first LED, said means for electrically connecting said at least one second LED, and said means for electrically connecting said at least one third LED.
 4. The voltage gradient detector of claim 2 wherein the separations S₁, S₂, and S₃ are the same length.
 5. The voltage gradient detector of claim 4 wherein the voltage threshold values V_(T1), V_(T2), and V_(T3) of said first, second, and third LEDs are the same.
 6. The voltage gradient detector of claim 5 wherein each of said first, second, and third LEDs is part of a photoMOS relay; and further wherein said means for providing a notice comprises: an alarm device activated by at least one of said photoMOS relays, said alarm device being selected from the group of: devices that generate an audible alarm; devices that emit a high-intensity light; devices that transmit an ultrasonic signal for reception by a remote receiver; and devices that transmit an electromagnetic signal for reception by a remote receiver.
 7. The voltage gradient detector of claim 6 wherein said alarm device transmits an ultrasonic signal for reception by a remote receiver, and further wherein said means for electrically connecting said at least one first, second, and third LEDs are sealably housed in spacer so as to make the detector suitable for use while submerged.
 8. The voltage gradient detector of claim 2 wherein said at least one first LED is connected across said first pair of electrodes and the separation S₁ is selected such that: S ₁ >V _(T1) /G _(MIN), whereby said at least one first LED is illuminated when said first pair of electrodes are exposed to a voltage potential therebetween that is at least as great as the threshold value V_(T1), thereby providing a voltage sufficient to illuminate said at least one first LED; further wherein said at least one second LED is connected across said second pair of electrodes and the separation S₂ is selected such that: S ₂ >V _(T2) /G _(MIN), whereby said at least one second LED is illuminated when said second pair of electrodes are exposed to a voltage potential therebetween that is at least as great as the threshold value V_(T2), thereby providing a voltage sufficient to illuminate said at least one second LED; and yet further wherein said at least one third LED is connected across said third pair of electrodes and the separation S₃ is selected such that: S ₃ >V _(T3) /G _(MIN), whereby said at least one third LED is illuminated when said third pair of electrodes are exposed to a voltage potential therebetween that is at least as great as the threshold value V_(T3), thereby providing a voltage sufficient to illuminate said at least one third LED;
 9. The voltage gradient detector of claim 2 wherein said means for electrically connecting said at least one first LED to said first pair of electrodes further comprises a first amplifier having a gain A₁, an input connected between said first pair of electrodes, and an output that provides a voltage to power said at least one first LED, where the output voltage equals the product of the input voltage and the gain A₁, the separation S₁ being selected such that: S ₁ *A ₁ >V _(T1) /G _(MIN); further wherein said means for electrically connecting said at least one second LED to said second pair of electrodes further comprises a second amplifier having a gain A₂, an input connected between said second pair of electrodes, and an output that provides a voltage to power said at least one second LED, where the output voltage equals the product of the input voltage and the gain A₂, the separation S₂ being selected such that: S ₂ *A ₂ >V _(T2) /G _(MIN); and yet further wherein said means for electrically connecting said at least one third LED to said third pair of electrodes further comprises a third amplifier having a gain A₃, an input connected between said third pair of electrodes, and an output that provides a voltage to power said at least one third LED, where the output voltage equals the product of the input voltage and the gain A₃, the separation S₃ being selected such that: S ₃ *A ₃ >V _(T3) /G _(MIN).
 10. The voltage gradient detector of claim 9 wherein the separations S₁, S₂, and S₃ are the same length, the voltage threshold values V_(T1), V_(T2), and V_(T3) are the same, and the amplifier gains A₁, A₂, and A₃ are the same.
 11. The voltage gradient detector of claim 9 wherein each of said first, second, and third pairs of electrodes has a discrete electrode and a common electrode, and wherein said common electrode is connected to each of said inputs of said first, second, and third amplifiers.
 12. The voltage gradient detector of claim 11 wherein said first, second, and third amplifiers are provided by a single multiple-amplifier device.
 13. A voltage gradient detector for use in water to detect the presence of a voltage gradient at least as large as a specified critical voltage gradient G_(MIN), the gradient detector comprising: a first pair of electrodes maintained at a separation S₁ along a first axis; at least one first LED with a known voltage characteristic such that said first LED is illuminated when it experiences a set voltage threshold value V_(T1); means for electrically connecting said at least one first LED to said first pair of electrodes such that said at least one first LED experiences a voltage that is directly responsive to the voltage between said first pair of electrodes and which is at least as great as the set voltage threshold value V_(T1) when said first pair of electrodes, spaced apart at the separation S₁, are in contact with a voltage gradient at least as great as the critical voltage gradient G_(MIN); a second pair of electrodes maintained at a separation S₂ along a second axis that is inclined to the first axis by an angle of between 45° and 135′; at least one second LED with a known voltage characteristic such that said second LED is illuminated when it experiences a set voltage threshold value V_(T2); means for electrically connecting said at least one second LED to said second pair of electrodes such that said at least one second LED experiences a voltage that is directly responsive to the voltage between said second pair of electrodes and which is at least as great as the set voltage threshold value V_(T2) when said second pair of electrodes, spaced apart at the separation S₂, are in contact with a voltage gradient at least as great as the critical voltage gradient G_(MIN); a third pair of electrodes maintained at a separation S₃ along a third axis that is inclined to the first axis by an angle of between 45° and 135°, and is inclined to the second axis by an angle of between 45° and 135′; at least one third LED with a known voltage characteristic such that said third LED is illuminated when it experiences a set voltage threshold value V_(T3); means for electrically connecting said at least one third LED to said third pair of electrodes such that said at least one third LED experiences a voltage that is directly responsive to the voltage between said third pair of electrodes and which is at least as great as the set voltage threshold value V_(T3) when said third pair of electrodes, spaced apart at the separation S₃, are in contact with a voltage gradient at least as great as the critical voltage gradient G_(MIN); and means for providing a notice when said at least one of said LEDs is illuminated.
 14. The voltage gradient detector of claim 13 wherein said first, second, and third pairs of electrodes are positioned such that, the second axis is inclined to the first axis by an angle of between 80° and 100′; and the third axis is inclined to the first axis by an angle of between 80° and 100°, and is inclined to the second axis by an angle of between 80° and 100°.
 15. The voltage gradient detector of claim 14 wherein each of said first, second, and third pairs of electrodes has a discrete electrode and a common electrode, and wherein said common electrode is connected to each of, said means for electrically connecting said at least one first LED, said means for electrically connecting said at least one second LED, and said means for electrically connecting said at least one third LED.
 16. A voltage gradient detector for use in water to detect the presence of a voltage gradient at least as large as a specified critical voltage gradient G_(MIN), the gradient detector comprising: a first pair of electrodes maintained at a separation S₁ along a first axis; at least one first LED with a known voltage characteristic such that said first LED is illuminated when it experiences a set voltage threshold value V_(T1); means for electrically connecting said at least one first LED to said first pair of electrodes in series with a first LED resistor such that said at least one first LED experiences a voltage that is directly responsive to the voltage between said first pair of electrodes and which is at least as great as the set voltage threshold value V_(T1) when said first pair of electrodes, spaced apart at the separation S₁, are in contact with a voltage gradient at least as great as the critical voltage gradient G_(MIN), wherein the set voltage threshold value V_(T1) is calculated by adding the minimum voltage that illuminates said at least one first LED and the voltage drop across said first LED resister that results from the current through said at least one first LED at that minimum voltage; a second pair of electrodes maintained at a separation S₂ along a second axis that is inclined to the first axis by an angle of between 45° and 135′; at least one second LED with a known voltage characteristic such that said second LED is illuminated when it experiences a set voltage threshold value V_(T2); means for electrically connecting said at least one second LED to said second pair of electrodes in series with a second LED resistor such that said at least one second LED experiences a voltage that is directly responsive to the voltage between said second pair of electrodes and which is at least as great as the set voltage threshold value V_(T2) when said second pair of electrodes, spaced apart at the separation S₂, are in contact with a voltage gradient at least as great as the critical voltage gradient G_(MIN), wherein the set voltage threshold value V_(T2) is calculated by adding the minimum voltage that illuminates said at least one second LED and the voltage drop across said second LED resister that results from the current through said at least one second LED at that minimum voltage; a third pair of electrodes maintained at a separation S₃ along a third axis that is inclined to the first axis by an angle of between 45° and 135°, and is inclined to the second axis by an angle of between 45° and 135′; at least one third LED with a known voltage characteristic such that said third LED is illuminated when it experiences a set voltage threshold value V_(T3); means for electrically connecting said at least one third LED to said third pair of electrodes in series with a third LED resistor such that said at least one third LED experiences a voltage that is directly responsive to the voltage between said third pair of electrodes and which is at least as great as the set voltage threshold value V_(T3) when said third pair of electrodes, spaced apart at the separation S₃, are in contact with a voltage gradient at least as great as the critical voltage gradient G_(MIN), wherein the set voltage threshold value V_(T3) is calculated by adding the minimum voltage that illuminates said at least one third LED and the voltage drop across said third LED resister that results from the current through said at least one third LED at that minimum voltage; and means for providing a notice when said at least one of said LEDs is illuminated.
 17. The voltage gradient detector of claim 16 wherein said first, second, and third pairs of electrodes are positioned such that, the second axis is inclined to the first axis by an angle of between 80° and 100′; and the third axis is inclined to the first axis by an angle of between 80° and 100°, and is inclined to the second axis by an angle of between 80° and 100°.
 18. The voltage gradient detector of claim 17 wherein each of said first, second, and third pairs of electrodes has a discrete electrode and a common electrode, and wherein said common electrode is connected to each of, said means for electrically connecting said at least one first LED, said means for electrically connecting said at least one second LED, and said means for electrically connecting said at least one third LED. 